Internally cooled bipolar radiofrequency ablation:: Is a lower power output more effective?

Purpose: Evaluation of bipolar radiofrequency (RF) ablation using internally cooled electrodes in an ex-vivo experiment. Materials and Methods: Bipolar RF ablations (n = 154) were performed in ex-vivo bovine liver. Both electrodes with a total length of the active tip of 4 cm were located on the same shaft of an internally cooled applicator. The power output was systematically varied between 20 and 100 watts (W). The energy application was continuous or modulated depending on the tissue resistance. In relationship to the maximum power output, the volume of coagulation was assessed. Results: In continuous energy application the induced volume of coagulation was increased at lower power outputs up to 33.7 cm(3) (20 watts). Parallel to an increased volume of coagulation, the required duration of energy application was increased up to a maximum of 51.6 minutes. Modulation of the power output as a function of the tissue resistance enabled application of a wide range of power outputs (40-75 watts) leading to a comparable extent of coagulation with a maximum of 14.9 cm(3) (10min.), 16.8 cm(3) (15 min.),and 19.1 cm(3) (20 min.). Conclusion: Continuous application of RF energy leads to an inverse relationship between volume of coagulation and power output. Modulation of the power output as a function of the tissue resistance enables application of a wider range of power outputs compared to continuous application of RIF energy.